Basic refractories

ABSTRACT

A basic refractory shape formed, for example, from dead-burned magnesia or dead-burned dolomite and having a high-carbon content is produced by heating a tar- or pitch-treated shape in the presence of vapors of a catalyst, such as an oxidation/polymerization agent, a polymerization/condensation agent or an inorganic oxidizing agent, and vapors of tar or pitch arising from the heating of the shape. The resulting shape can be fired to carbonize the tar or pitch. Impregnation with further quantities of tar or pitch subsequent to heating with the catalyst vapors is optionally effected before firing.

O Umted States Patent [151 3,640,5 18 Lythe et al. 1 Feb. 8., 1972 [5BASIC REFRACTORIES [5 References Cited [72] Inventors: Trevor WilkinsonLythe, Worksop; Ed- UNITED STATES PATENTS fl Norm NW0", 3,061,451l0/l962 Parker et al ..264/345 X both of England 2,699,931 1/1955 Buhleret al. ..263/52 I 73] Asmgncc: bleetley (Mfg) Ltd., Worksop, EnglandPrimary Emmmu lohn L Camby [22] Filed: Apr. 15, 1970 Altorney-Bacon &Thomas 1 pp N 28,977 57 ABSTRACT A basic refractory shape formed, forexample, from dead- [30] Foreign Application Priority Data burnedmagnesia or dead-burned dolomite and having a highcarbon content isproduced by heating a taror pitch-treated Apr. 18, 1969 Great Bntam..20,01 5,69 shape in the presence f vapors of a catalyst, such as anOxida don/polymerization agent, a polymerization/condensation [52] US.CL ..'.....263/52, 264/345 agent or an inorganic oxidizing agent, andvapors of tar or [51] Int. C F274! 1/04 pitch arising from the heatingof thevshape. The resulting [581 mm of Search ..263/52; 264/345 shapecan be fired to Carbonize the tar or p impregnation with furtherquantifies of tar or pitch subsequent to heating with the catalystvapors is optionally effected before firing.

13 Claims, N0 Drawings 1 Basic REFRACTORIES FIELD OF INVENTION Theinvention relates to a process for making improved basic refractoryshapes and to the product thereof.

The advent of basic steelmaking processes using oxygen has demanded newand improved refractory lining materials for the vessels used intheseprocesses. This has resulted in the development of tarorpitch-impregnated fired basic bricks. The bricks are usually made fromdead-bumed dolomite (doloma) dead-burned magnesite (magnesia) ormixtures of the two materials. Specifically graded fractions of thematerials are used with a transient bond which serves to make the brickor block suitable for handling after pressing usually to 8-10 tons/sq.in. The pressed bricks are subsequently dried at a temperature of l-300C. for a period of 24 hours and then fired to a high temperature,usually in the range 1,400-l ,800 C., to develop a ceramic bond. Ifthese bricks are impregnated after firing with tar or pitch so that allthe open pores in the bricks are filled, then this type of brick gives abetter performance in service in steel making vessels which come intocontact with oxygen than that given by bricks which have not beenimpregnated with tar or pitch.

in service the tar or. pitch carbonizes and the residual carbon has abeneficial effect by restricting the ingress of slag by both a physicaland chemical action. By progressively increasing the residual carboncontent of the brick, the attack by the slag produced in the steelmakingprocess, is progressively reduced, thereby increasing the serviceperformance of the brick.

DESCRIPTION OF THE PRIOR ART The normal method of impregnating firedbasic refractories with tar or pitch is to heat the fired bricks toapproximately 300 C. and then to transfer the hot bricks to avacuum/pressure vessel and to remove the air in the bricks byevacuation. Tar or pitch preheated to a temperature such that itsviscosity is suitable for impregnating the pores of the brick is thenpumped into the evacuated vessel. Normally the viscosity must be lessthan that which produces a flow out time of 18 seconds through anS.T.P.T.C. 4 mm. tar viscometer cup, and preferably less than that whichproduces a flow out time of l2 seconds. The exact method is described inStandard Methods of Testing Tar and Its Products" 6th Edition-- I 967published by the Standardisation of Tar Products Tests Committee,Gomersall, Cleckheaton, Yorkshire. After l-2 hours the vessel ispressurized for a short time to complete the impregnation. The pressurein the vessel is then returned to that of the atmosphere. The hot tar orpitch is then pumped out of the vessel and the impregnated bricks areremoved and cooled and are then ready for building into the steel makingvessel. This or any other method may be used to make the tar or pitchimpregnated bricks or shapes used in the process of the invention whichdescribed hereinafter.

Chemical additives, particularly oxidation/polymerization agents orpolymerization/condensation agents, can be used to increase the carbonretention properties of tars or pitches. Unfortunately if added directlyto the tar or pitch they increase its viscosity in the temperatureranges normally employed in the impregnation process i.e., 40-200 C. sothat their use becomes practically difficult.

SUMMARY We have now discovered that by exposing taror pitchtreatedshapes, such as taror pitch-impregnated bricks, to the vapor phase of acatalyst, a substantial increase in carbon retention after firing maybe'achieved.

According to the present invention there is provided a process for theproduction of a basic refractory shape which, when fired, has a highcarbon content, which process comprises heating a taror pitch-treatedshape in the presence of the vapors of a catalyst and vapors of tar orpitch arising from the heating of the taror pitch-treated shape. Theshape so obtained is preferably allowed to cool before being fired.

THE PREFERRED EMBODIMENTS OF THIS INVENTION The taror pitch-treatedshape may be a taror pitch-impregnated shape or a taror pitch-bondedshape.

The basic refractory material from which the shape is made may be deadburned or fused magnesia, dead burned or fused lime or mixtures of thesesuch as dead burned or fused dolomite. Dead-burned magnesia, dead-burneddolomite and mixtures thereof are especially preferred.

The firing step may form part of the process of the present invention ormay take place during service when, for example, the shapes form part ofa furnace structure. In the former case firing may be achieved byheating the shape in a reducing atmosphere, for example while embeddedin carbon, to a temperature (usually in excess of 500 C.) such that thecarbon content of the tar or pitch remaining after heating is greatlyincreased and very little volatile matter remains.

In the process of the present invention the heating of the tarorpitch-treated shape involves some increase in carbon content of the taror pitch and a decrease in the quantity of tar volatiles in the shapebut does so on a significantly smaller scale than in firing. Desirablythe taror pitch-treated shape is heated to a temperature in the rangel50l ,000" C.

The catalyst used in the process of the present invention is a materialwhich, when mixed with tar or pitch, generally has the effect ofincreasing their viscosity. Such catalysts include organic material forexample oxidation/polymerization agents or polymerization/condensationagents such as aromatic sulphonyl halides, aromatic and heterocyclicalcohols and aldehydes and aromatic nitrocompounds or compatiblemixtures thereof. Typical aromatic nitrocompounds include nitrobenzene,m-dinitrobenzene, nitrotoluene, dinitrotoluene, trinitrotoluene anddinitronophthalene. The catalyst may also be an inorganic oxidizingagent such as ammonium persulphate, potassium permanganate, potassiumdichromate or sodium nitrate. Certain salts are also effective, such asaluminum chloride, zinc chloride and ferric chloride.

The heating of the taror pitch-treated shape may he car ried out in aclosed oven or one with a closed circulation system. The catalyst may beinjected into the oven as a vapor or as a liquid which is subsequentlyvaporized in the oven. The catalyst may also be placed in the oven insolid or liquid form along with the shapes and vaporized while in theoven.

In one embodiment of the invention treatment of the shape with vapors ofthe catalyst is carried out by placing the shape above the surface of arefluxing solution or suspension of the catalyst in tar or pitch.

In an improvement of the present invention it has been found that thecarbon content after firing can be increased further if, after heatingthe taror pitch-treated shape in the presence of the catalyst vapors,the shape is impregnated, before or after cooling, with furtherquantities of tar or pitch. This increase is greater than would beanticipated.

The process of the present invention is not limited to onereimpregnation with tar or pitch provided that the shape is heated aftereach impregnation step. Accordingly the present invention also providesa process as described above wherein, after impregnation with furtherquantities of tar or pitch, the additional steps of heating andimpregnating with tar or pitch are effected one or more times. Theheating steps may be carried out in the presence of a vaporizedcatalyst. While it is desirable to carry out the first heating of thetaror pitch-impregnated shape at a temperature in the range l 50l ,000"C., it is preferred to carry out a second heating step at a temperatureof l75-l,000 C. and a third heating step at a tempera- The catalystemployed in this embodiment may be concentrated nitric acid, ammoniumpersulphate, p-toluene sulphonyl chloride, furfuryl aldehyde orm-dinitrobenzene and the taror pitch-impregnated or taror pitch-bondedshape is preferably formed from dead-burned magnesia, dead-burneddolomite or a mixture thereof. The shape may be fired after cooling. i

Finally the present invention provides a basic refractory shape, such asa brick, when produced by the method described above.

Before giving examples of our invention it is pertinent to describe themethod used to determine the carbon retention of taror pitch-treatedbricks:

Samples cut from the treated brick are weighed (Wa) and then embedded incarbon granules contained in a chamber which can be sealed so as toobtain an atmosphere devoid of free air and oxygen. The chamber isheated by means of external silicon carbide heating elements. Thesamples are heated up to 800 C. at the following rate:

20-200 C.; 220 C./hour 200-500 C.; 100 C./hour 500800 C; 60 C./hour Whenthe samples attain a temperature of 800 C. the furnace is switched offand allowed to cool to room temperature. This is commonly referred to ascoking and converts all the tar or pitch to carbon. The samples areremoved, weighted (Wb) and then ignited at l,000 C. to constant weightin an electrically heated furnace having an atmosphere containing freeair and oxygen. The cooled carbon free samples are finally weighed (We).

% Carbon retained (WbWc)/Wb Total Tar or pitch in block (Wa-Wc )lWa Theinvention will now be illustrated with reference to the followingexamples. In these examples the carbon retention 5 after coking by theprocedure described above must be compared with that of the standardblock treated with tar or pitch only.

EXAMPLE 1 A series of fired magnesia bricks of the following chemicalanalysis was produced in the laboratory:

CONSTITUENTS wr.

sio, 0.35 A120: 0.21 n.0, 0.1 s CaO 1.00 Tio 0.01 M11 0, 0.01 0,0, 0.303,0, 0.02 M30 0085 PROPERTY VALUE Melting Point (Ring and Ball) "C. 93Specific Gravity at 15.5 C. L30 lnsolubles (a) In Toluene Wt.% 27.0 (b)In Quinolinc Wt.% 5.5 Ash Content Wt.% 0.20 Coking Value (Alcan Method)Wt.% 52

After impregnation and cooling, the bricks were separately placed inrefluxing vessels and the temperature raised to the range I l0-425 C.the temperatures being specifically selected for each of the agentsunder investigation. After refluxing for specific lengths of time thebricks were cooled and then coked" in the manner previously describedand their carbon retentions determined. The effect of these vapor phasetreatments and the resultant retained carbon content of the bricks isshown in Table I.

TABLE I Vapor Phase Catalyst Carbon Retention Wt. 1-

Agent Reflux Reflux NO 4 Reimpregnution Temp. Time lmpl'egnallon ofStoved "c. Hours After Bricks With Smvins Pitch Nil 2.7 Meta 8 3.5 4.3Dinitrobcnzcnc 420-425 12 3.6 4.5 Nil 420-425 8 3.2 3.8

l2 3.3 4.0 Dinitrotoluene 420-425 8 3.5 4.3

Meta Dinitrobeniene 300-305 8 3.3 3.8

Nil 300-305 8 3.0 3.3

12 3.1 3.5 Dinitrotolucnc 300-305 8 3.4 3.9

l2 3.6 4.1 Furfuryl Aldehyde 300-305 8 3.4 3.9

12 3.6 4.1 Furfuryl -175 a 3.1 .14 Aldehyde 12 3.4 3.0 Nil l70-l75 8 2.72.7

Para Toluene Sulphonyl [45-150 8 30 ll Chloride l2 3.0 3.3 Nil l45-l50 82.7 2.7

l 2 2.7 2.7 Ammonium ll0-l l5 8 3.0 3.2 Pcrsulphatc l2 3.! 3.3 Nil ll0-ll5 8 2.7 2.7

l 2 2.7 2.7 Nitric Acid' I20-| 25 4 3.0 3.3

EXAMPLE 2 A series of fired magnesia bricks having the chemical analysisand apparent porosity quoted in Example I were produced in thelaboratory. These bricks were impregnated by the,

vacuum/pressure process hereinbefore described with a tar having thefollowing properties:

After impregnation with tar the bricks were treated as described inExample 1 and the effects of the treatments on the resultant retainedcarbon content of the bricks is shown in Table 2.

It should be noted-that the process described is equally applicable totaror pitch-bonded basic materials i.e., products which have not beenfired and impregnated but which are graded, mixed fractions of dolomaand/or magnesia mixes pressed into shape with a tar or pitch bond. Thisis illustrated in Example 3.

EXAMPLE 3 Batches (60lb.) of burned dolomite were crushed through aiii-inch B.S. mesh and graded as follows:

B.S. Mesh Wt. '56

3/s" +1 4" l8 |/4" +3116" 12 3ll6"+5 r -5 +7 10 -7 +14 10 -14 +25 10 -25+72 10 -72 (Ball milled 0.27 mlgm specific surface) Each batch washeated to a specific temperature before being fed into a preheated panmill. The grain preheat temperature for pitch-bonded blocks was 200 C.and for tar bonded blocks was 120 C. The tar preheat temperature was 120C. and the pitch preheat temperature was 180 C. The heated tar or pitchwas added until the batch achieved the required consistency forhydraulic pressing and the batch mixed for 10 minutes. The hot batch wasthen pressed into four 9X4.5X3 inch (228Xl14X76 mm.) blocks at 8t.p.s.i. (123.5 MN/m?) on a hydraulic press. These blocks were stored at300 C. in the presence of dinitrotoluene vapor. The effect of the vaporphase treatments on retained carbon content is illustrated in Table 3.

TABLE 3 Bond Tar C Retention After Type Dinitrotoluene Content StovingAt Wt. Vapor Wt. Wt. 800 C. 1.000 C.

5.0 3.1 1.2 EVT 60 0.15 5.0 4.3 2.3 Tar 5% 0.30 5.0 4.4 2.4

0.50 5.0 4.5 2.6 0.80 5.0 4.5 2.7 6.7 4.1 3.4 Ring and Bull 0.50 6.7 5.54.4 C. Pitch 0.30 6.7 5.6 4.5

We claim:

1. In a process for the production of a basic refractory shape which,when fired, has a high carbon content. wherein said shape has beentreated with a member selected from the group consisting of tar andpitch. the improvement which comprises heating said treated shape in thepresence of vapors of a catalyst and vapors of the member selected fromthe group consisting of tar and pitch arising from the heating of saidtreated shape.

2. The process of claim 1 wherein said treated shape is selected fromthe group consisting of a tar-impregnated shape, a pitch-impregnatedshape, a tar-bonded shape and a pitchbonded shape.

3. The process of claim 1 wherein the shape is subsequently fired in areducing environment.

4. The process of claim 3 wherein the shape is fired while embedded incarbon.

5. The process of claim 1 wherein said treated shape is heated to atemperature of from to l,000 C. in an oven selected from the groupconsisting of a closed oven and an oven with a closed circulationsystem.

6. The process of claim 1 wherein the catalyst is selected from thegroup consisting of an oxidation/polymerization agent, apolymerization/condensation agent and an inorganic oxidizing agent.

7. The process of claim 1 wherein the catalyst is selected from thegroup consisting of an aromatic sulphonyl halide, an aromatic alcohol,an aromatic aldehyde, a hcterocyclic alcohol, a heterocyclic aldehyde,an aromatic nitrocompound and mixtures thereof.

8. The process of claim 1 wherein the catalyst is selected from thegroup consisting of nitrobenzene, m-dinitrobenzcne, nitrotoluene,dinitrotoluene, trinitrotolucne. dinitronaphthalene, ammoniumpersulphate, potassium permanganate, potassium dichromate, sodiumnitrate, aluminum chloride, zinc chloride, ferric chloride, furfurylaldehyde, ptoluene sulphonyl chloride and nitric acid.

9. The process of claim 1 wherein the treated shape is impregnated witha further quantity of a member selected from the group consisting of tarand pitch after being heated in the presence of catalyst vapors.

10. The process of claim 9 wherein, after impregnation with a furtherquantity of a member selected from the group consisting of tar andpitch, the additional steps of heating and impregnating with a memberselected from the group consisting of tar and pitch are effected atleast one more time.

11. In a process for the production of a basic refractory shape which,when fired, has a high carbon content and wherein said shape is selectedfrom the group consisting of a tar-impregnated shape, apitch-impregnated shape, a tarbonded shape and a pitch-bonded shape theimprovement which comprises heating said shape in the presence of vaporsof a catalyst and vapors of a member selected from the group consistingof tar and pitch arising from the heating of said shape and thereaftercooling the shape.

12. The process of claim 11 wherein the shape is fired after beingcooled.

13. The process of claim 11 wherein the catalyst is selected from thegroup consisting of concentrated nitric acid, ammonium persulphate,p-toluene sulphonyl chloride, furfuryl aldehyde, m-dinitrobenzene andmixtures thereof.

2. The process of claim 1 wherein said treated shape is selected from the group consisting of a tar-impregnated shape, a pitch-impregnated shape, a tar-bonded shape and a pitch-bonded shape.
 3. The process of claim 1 wherein the shape is subsequently fired in a reducing environment.
 4. The process of claim 3 wherein the shape is fired while embedded in carbon.
 5. The process of claim 1 wherein said treated shape is heated to a temperature of from 150* to 1,000* C. in an oven selected from the group consisting of a closed oven and an oven with a closed circulation system.
 6. The process of claim 1 wherein the catalyst is selected from the groUp consisting of an oxidation/polymerization agent, a polymerization/condensation agent and an inorganic oxidizing agent.
 7. The process of claim 1 wherein the catalyst is selected from the group consisting of an aromatic sulphonyl halide, an aromatic alcohol, an aromatic aldehyde, a heterocyclic alcohol, a heterocyclic aldehyde, an aromatic nitrocompound and mixtures thereof.
 8. The process of claim 1 wherein the catalyst is selected from the group consisting of nitrobenzene, m-dinitrobenzene, nitrotoluene, dinitrotoluene, trinitrotoluene, dinitronaphthalene, ammonium persulphate, potassium permanganate, potassium dichromate, sodium nitrate, aluminum chloride, zinc chloride, ferric chloride, furfuryl aldehyde, p-toluene sulphonyl chloride and nitric acid.
 9. The process of claim 1 wherein the treated shape is impregnated with a further quantity of a member selected from the group consisting of tar and pitch after being heated in the presence of catalyst vapors.
 10. The process of claim 9 wherein, after impregnation with a further quantity of a member selected from the group consisting of tar and pitch, the additional steps of heating and impregnating with a member selected from the group consisting of tar and pitch are effected at least one more time.
 11. In a process for the production of a basic refractory shape which, when fired, has a high carbon content and wherein said shape is selected from the group consisting of a tar-impregnated shape, a pitch-impregnated shape, a tar-bonded shape and a pitch-bonded shape the improvement which comprises heating said shape in the presence of vapors of a catalyst and vapors of a member selected from the group consisting of tar and pitch arising from the heating of said shape and thereafter cooling the shape.
 12. The process of claim 11 wherein the shape is fired after being cooled.
 13. The process of claim 11 wherein the catalyst is selected from the group consisting of concentrated nitric acid, ammonium persulphate, p-toluene sulphonyl chloride, furfuryl aldehyde, m-dinitrobenzene and mixtures thereof. 